During a menstrual cycle each month, the body typically grows one follicle that will mature and eventually release an egg. The body will also secrete estrogen and progesterone to thicken the lining of the uterus, the endometrium, to support the egg if it fertilizes. If fertilization does not occur, the endometrium will shed in the form of your monthly period. Typically, a woman has her period every 21 to 35 days, lasting between two to eight days. However, some women have hormonal imbalances preventing ovulation that cause women to skip or have irregular periods.